1. Field of the Invention
The present invention pertains to a system and method for injecting a mixture of water and gas into a subterranean earth formation for storing the gas in the formation and for enhancing the recovery of hydrocarbon fluids from the formation.
2. Background
Reinjection of gases produced from subterranean earth formations has been carried out as a method of storing the gas for future production and for stimulating the production of hydrocarbon liquids such as crude oil. In certain earth formations the injection of gas alone will quickly result in migration of the gas towards oil production wells thereby disrupting the effective production of oil, particularly if the quantities of gas migrating are substantial, and resulting in unwanted production of the gas back to the surface.
In certain earth formations such as those found in the North Slope Oilfields of the State of Alaska mobility control over the flow of gas after reinjection into a formation has been provided by alternately injecting water and then gas into the formation. Reduced mobility without serious loss of use of the gas as a stimulant for the production of oil has been carried out with some effectiveness. However, the cost of providing separate water and gas injection piping networks leading to each injection well can become prohibitive and the alternate injection of slugs of water followed by slugs of gas, or vice versa, is not believed to be as effective in reducing the gas mobility within the formation as may be obtained if a mixture of water and gas is injected into the formation. Hence, simultaneous water and gas injection is believed to be desirable.
However, certain problems arise in providing for simultaneous water and gas injection into subterranean earth formations through injection wells. For example, uniform distribution of the gas and liquid mixture is difficult to obtain when the mixture must be transported long distances through piping networks and manifolds. Accordingly, the present invention is directed to a system which will provide effective injection of a uniform mixture of water and gas into selected injection wells to effectively control the mobility of the injected gas so that the earth formation serves as a gas storage reservoir while permitting at least some of the gas to migrate sufficiently through the reservoir to serve as a drive fluid to increase the yield of liquid hydrocarbons from the formation through production wells.